The package included photos -- but no images of the shootings. The items were delivered to NBC this morning and were immediately turned over to FBI agents in New York.

In a manifesto, included in the package, Cho refers to the two killers behind the shootings at Columbine High School as "martyrs."

The package was postmarked at 9:01 AM ET Monday -- about an hour and 45 minutes after police say Cho shot two people at a residence hall, and shortly before he entered another campus building and killed 30 more, before turning the gun on himself.